linux-kernel - Re: [PATCH] msi-x: let drivers retry when not enough vectors

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Message-ID: <20090507090506.GB32039@redhat.com>
Date:	Thu, 7 May 2009 12:05:06 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Sheng Yang <sheng@...ux.intel.com>
Cc:	kvm@...r.kernel.org, jbarnes@...tuousgeek.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	Matthew Wilcox <willy@...ux.intel.com>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] msi-x: let drivers retry when not enough vectors

On Thu, May 07, 2009 at 04:51:24PM +0800, Sheng Yang wrote:
> On Thursday 07 May 2009 16:28:41 Michael S. Tsirkin wrote:
> > pci_enable_msix currently returns -EINVAL if you ask
> > for more vectors than supported by the device, which would
> > typically cause fallback to regular interrupts.
> >
> > It's better to return the table size, making the driver retry
> > MSI-X with less vectors.
> 
> Hi Michael
> 
> I think driver should read from capability list to know how many vector 
> supported by this device before enable MSI-X for device, as 
> pci_msix_table_size() did...

Drivers can do this, but it's more code. Since pci_enable_msix
calls pci_msix_table_size already, let it do the work. Right?


> -- 
> regards
> Yang, Sheng
> 
> >
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > ---
> >
> > Hi Jesse,
> > This came up when I was adding MSI-X support to virtio pci driver,
> > which does not know the exact table size upfront.
> > Could you consider this patch for 2.6.31 please?
> >
> >
> >  drivers/pci/msi.c |    6 +++---
> >  1 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> > index 6f2e629..f5bd1c9 100644
> > --- a/drivers/pci/msi.c
> > +++ b/drivers/pci/msi.c
> > @@ -687,8 +687,8 @@ int pci_msix_table_size(struct pci_dev *dev)
> >   * indicates the successful configuration of MSI-X capability structure
> >   * with new allocated MSI-X irqs. A return of < 0 indicates a failure.
> >   * Or a return of > 0 indicates that driver request is exceeding the
> > number - * of irqs available. Driver should use the returned value to
> > re-send - * its request.
> > + * of irqs or MSI-X vectors available. Driver should use the returned
> > value to + * re-send its request.
> >   **/
> >  int pci_enable_msix(struct pci_dev* dev, struct msix_entry *entries, int
> > nvec) {
> > @@ -704,7 +704,7 @@ int pci_enable_msix(struct pci_dev* dev, struct
> > msix_entry *entries, int nvec)
> >
> >  	nr_entries = pci_msix_table_size(dev);
> >  	if (nvec > nr_entries)
> > -		return -EINVAL;
> > +		return nr_entries;
> >
> >  	/* Check for any invalid entries */
> >  	for (i = 0; i < nvec; i++) {
> 

-- 
MST
--
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